Few topics within the antitrust bar have yielded more lively and sustained analysis over the past decade than the issue of class certification under Rule 23. Yet virtually all of that analysis has focused on just one-half of the class action device: the plaintiff class action. In an article published in Bloomberg BNA’s Class Action Litigation Report, Hollis Salzman, partner and co-chair of the Antitrust and Trade Regulation practice at Robins Kaplan LLP, and associate Ben Steinberg discuss the lesser-used, but equally viable flipside of Rule 23: the so-called defendant class action. This article seeks to fill a void in literature by reviewing how courts to date have treated defendant class actions in the antitrust context. The authors find that despite its infrequent usage, the defendant class action can serve as a useful tool for antitrust litigators in cases involving large numbers of defendants, particularly where anticompetitive conduct is facilitated by trade associations or other industry groups. The authors argue that the defendant class action therefore provides a window of opportunity for plaintiffs’ attorneys and warrants deeper consideration than what has previously been afforded.